[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)

Yes Imean between carb and outside world:-) But the engine keept running the first time if I put this cone on it, but doesent matter what did you mean with injection system?

An injection system does not get confused by the pressure fluctuations in the intake tract, like a carburettor does. You will have noticed that the mixture can become richer or weaker without any changes in the carburettor settings, when you fit stiffer or softer reeds in a reedvalve-engine. So each time you change the reed thickness (or the length of the intake tract), you must also re-adjust the carburation. And with an experimental set-up like the 24/7-valve it may be even more critical.
With an injection system you would not need to re-adjust each time. So you might want to ask Santa Claus....

thats clear in now verry well witch are the benefits of an injection system,i wanted more asking for if you dont know somthing wats possible to by or perhaps you got an injction system for two strokes wich is well working?

Michael Burgard a écrit:

thats clear in now verry well witch are the benefits of an injection system,i wanted more asking for if you dont know somthing wats possible to by or perhaps you got an injction system for two strokes wich is well working?

No, I haven't got an injection system of my own, but this one looks good to me: [Vous devez être inscrit et connecté pour voir ce lien] .
There are a lot of products on the market; just ask Google. Or you can ask Claus Bernecker the next time he comes over for a cup of coffee . He knows a lot about injection.

Frits, Did you ever experiement with injection on the RSA/RSW? Especialy since a system is so cheap now.
I suppose because 125 is operating at 100% throttle most of the time, the carburetor is a bit immune to the inlet resonance?

Frits
Avez-vous déjà experiement avec injection sur le RSA / RSW? Spécialement depuis unsystème est si bon marché maintenant. Je suppose que 125 fonctionne à 100% de gaz la plupart du temps, le carburateur est un peu à l'abri de la résonance d'entrée?

Thats great, to see how small the world is
I will try today the inlet at the dyno under restpect the information you given to me,and tell you this evening how it was working......

Michael, i've sent you through private message a little excel open office sheet that i wrote down, that should help you determine the optimal lenght.
If anybody wants it just let me know.

make this valve work!

I'm going to try it too, actuated with a stepper motor.

nasone32 a écrit:

Michael, i've sent you through private message a little excel open office sheet that i wrote down, that should help you determine the optimal lenght.
If anybody wants it just let me know.

make this valve work!

I'm going to try it too, actuated with a stepper motor.

yes please - can you send this to me as well? thanks nasone32

[quote="nasone32"]Michael, i've sent you through private message a little excel open office sheet that i wrote down, that should help you determine the optimal lenght.
If anybody wants it just let me know.[quote]

For me also please, thank you.

Institute of TwoStrokes a écrit:

Frits, did you ever experiment with injection on the RSA/RSW? Especialy since a system is so cheap now. I suppose because 125 is operating at 100% throttle most of the time, the carburetor is a bit immune to the inlet resonance?

The last experiments with injection on anAprilia two-stroke racer were with the RS500 twin, ridden by Jeremy McWilliams. It had two injectors per cylinder: one in the intake tract and one in the crankcase. Throttle response was ....ehh .... sudden! Fortunately Jeremy was a very brave rider.
This system was never tried on the 125. I think it could have been developed into something good, but when the competition in the 125 and 250 cc classes gave up, the development of the Aprilias stopped. Why spend money when you are winning anyway? (to learn, but you cannot explain that to an accountant).

The carburation of a disk-valve engine is less sensitive to inlet resonances than that of a reed-valver. And it is far less sensitive to exhaust resonances. I have seen that on the Cagiva 500-4. First it had piston induction, then it got disk valves, and finally reed valves. The disk-valve engine was fairly rideable but its successor was not a pleasant bike, especially in the wet.
On a reed-valve engine the reeds are opened by the suction from the exhaust pipe. When you close the throttle, the energy flow to the exhaust stops, and thus the suction stops.
When you open the throttle again, nothing happens because the exhaust suction is absent; the reeds stay closed and there is nothing in the cylinder to combust. So the rider opens the throttle a bit more, and a bit more, and a bit... and then there is enough mixture in the cylinder to start combustion again. But now the throttle is wide open: Whamm, high-sider!
In a disk-valve engine the disk always opens, combustion or no combustion. So, contrary to popular belief, it is much easier to ride than a reed-valver.
(The Cagiva was cured by inserting 1 mm strips between the reed casing and the reeds, so the reeds did not really close anymore. It cost more than 10 hp, but the laptimes improved...
Because of those 'leaking' reeds setting the carburation was a nightmare. So Cagiva concentrated on injection, and got fairly good results.)

@ nasone32 Thanks for the exel sheet
but my biggest problem at the moment its Time!I only start this project because I love so much the idea behind and I couldent wait anymore too see whats happend if I fit such a kind of valve at one of my engines.I think I will got more time for this project in January.So I will do some trys with the vale this evening,and than I got to set it aside....even if I want to continue, this will be not possible at the moment because there are other projects wich I got to finish for production..

greetings from Germany Michael

from what i've learned, the lenght you should put in the sheet is from the tip of the reed to about 10mm out of the carb bellmouth. this should be where the wave reflection takes place.
so keep this in mind...
please share your results in terms of data, it would really help to validate everything.
the cone before the carb makes things more difficult since i don't know where the wave would really reflect... as Frits said I think a short bellmouth makes everything easier.

edit: the cone should also make the reflected wave less sharp than a short bellmouth...

Citation :

If anybody wants it just let me know.

+1

Nasone, if you calculate the intake length based on wave motion, then let us take a look at what happens in the engine.
When the transfer ports are open, the exhaust sucks mixture out of the crankcase. Shortly afer BDC the crankcase pressure becomes less than atmosferic. Now a suction wave starts moving from the crankcase through the intake tract in the direction of the open air.
When it reaches the open end of the intake tract, it reflects and returns as a pressure wave to the crankcase, where it should arrive just in time for the next cycle.
So during 1 crankshaft revolution the wave should move up and down through the intake tract once.

Now comes the nasty part.
In cold mixure the speed of sound is about 300 m/s.
Let us assume an engine speed of 12.000 rpm. Then 1 crankshaft revolution takes 0,005 second.
During this time the wave travels 0,005 * 300 = 1,5 meter. Once up and down the intake tract is 1,5 m, so the tract length must be 0,75 meter; theoretically correct, but not very practical....
In reality the intake length will be in the order of 0,125 m. That means the wave will travel up and down 6 times. 6 times it is reflected at the carburettor bellmouth and 6 times it is reflected at the crankcase side of the tract. But after these 12 open end-reflections you can be sure that the wave hast lost all of its energy :| ...

So calculating the tract length based on wave movement is pointless. But there is another way of calculating: do not look at the wave motion through the mixture, but look at the mass movement of the mixture itself: the Helmholtz-resonance.
It would take up too much forum space to explain this phenomenon here, but the essentials are:
a bigger crankcase volume lowers the Helmholtz-frequency, a longer intake tract also lowers this frequency, and a larger tract diameter raises the frequeny. That is why I asked the carburettor diameter and suggested using exchangeable distance pieces between carburettor and valve.

I hope I have not discouraged you. But two-strokes are not simple; they only seem simple...

@Michael Burgard: could you shoot a video of your 24/7-engine running? I would love to see it and I am sure Nasone would love to show it to his opponent on the Italian forum

My spreadsheet allows calculation of both helmholtz and wave resonance of course
this morning I have also written to michael to take in account only helmholtz because it it surely the most important.

Frits I'll explain it for you very simple, i have an idea!
The air in the crankcase is compressible and have some elasticity (right?) and the air in the intake has a certain mass.
so it would like to oscillate at a certain frequency like the mass and the spring in this animation
[Vous devez être inscrit et connecté pour voir cette image]

the engine runs at its own frequency so making both the same makes us happy
or the helmholtz frequency can be a multiple of the frequency of the engine.

in a reed valved engine (not 24/7) we must also take in account the phase of the reeds opening wich is a bit tricky, i find my own by simulation but you can bet on high performance engine is somewhere between 240 and 270 degrees.

yes i would be glad to see the video too

In cold mixure the speed of sound is about 300 m/s.

Frits - why do you assume the speed of the mixture is equal to the speed of sound? as there is mass involved, I would would say that the mass needs to accelerate, get on speed, then deccelerate, stop and reverse, causing a substantial delay in speed.

I apologize, Nasone. I only had your text to go by, and from that I concluded that you only took the wave action into consideration.

nasone32 a écrit:

the engine runs at its own frequency so making both the same makes us happy or the helmholtz frequency can be a multiple of the frequency of the engine.

Having a Helmholtz frequency that is a multiple of the engine breathing frequency would be an unnecessary waste of energy because the amplitude weakens with every change of direction. I say unnecessary because it is always possible to lower the Helmholtz frequency to the desired fundamental value.

Citation :

in a reed valved engine (not 24/7) we must also take in account the phase of the reeds opening wich is a bit tricky, i find my own by simulation but you can bet on high performance is somewhere between 240 and 270 degrees.

Those angles are realistic. But I claim that in a normal reed-valved engine you have no real Helmholtz frequency; once the flow direction wants to reverse, it is blocked by the reed. It would be the same as a brake that stops the bouncing mass in your animation once it has reached its highest position.
Only two things can go wrong in a reed-valve engine. With too low a Helmholtz frequency the mixture column in the intake tract has no chance to convert all of its kinetic energy into pressure before the next cycle starts. Or the frequency can be so high that the flow already reverses before the crankcase volume has reached its maximum value (piston in TDC). Between these two extremes there is a broad frequency range that functions well in combination with reed valves.

Hi Guys,
I im just finished testing befor an 1/2 hour.I receved to make it working a littel better than yesterday but allready not perfekt at all... I tried also a short cone before the carb but it dosent really chaged something,but I continued with the small cone before the carb. So I continued working at the carb setting itself, with a little bit of succes.So I was doing some runs at the dyno, and it was not so bad for the first time with such an inlet valve. I did a screen shot of the dynocharts because I couldent upload the original data.The red curve is the 24/7inlet the other one is with reed valve. The Performance was mesured at the back wheel.

Sorry for the video but I readed the request for the video too late, but on the dynosheet you can see really good if the valve get open and whats happend.

[Vous devez être inscrit et connecté pour voir ce lien]

jenne smit a écrit:

In cold mixure the speed of sound is about 300 m/s. Frits - why do you assume the speed of the mixture is equal to the speed of sound? as there is mass involved, I would would say that mass needs to accelerate, be on speed, then decelerate, stop and reverse, causing a substantial delay in speed.

I do not assume that, Jenne. You are absolutely right about the behaviour of the mass, but I was not talking about the mass; I was talking about the wave that runs throught the mass - with the speed of sound, by definition.
The mass itself moves much slower; its mean velocity in the intake tract is less than half the speed of sound.
(If there are any gas dynamic specialists reading in: yes, suction waves move with subsonic speed and pressure waves with supersonic speed, dependent on the magnitude of their amplitude, but for now let's keep it simple ).

Michael Burgard a écrit:

I im just finished testing befor an 1/2 hour.I receved to make it working a littel better than yesterday but allready not perfekt at all... I tried also a short cone before the carb but it dosent really chaged something,but I continued with the small cone before the carb. So I continued working at the carb setting itself, with a little bit of succes. The red curve is the 24/7 inlet the other one is with reed valve.

90% of the original power and a power gain at hight revs after only a few days of experimenting is highly encouraging.
I haved filed your dyno chart in the map 'historic documents'

Frits Overmars a écrit:

jenne smit a écrit:

In cold mixure the speed of sound is about 300 m/s. Frits - why do you assume the speed of the mixture is equal to the speed of sound? as there is mass involved, I would would say that mass needs to accelerate, be on speed, then decelerate, stop and reverse, causing a substantial delay in speed.

I do not assume that, Jenne. You are absolutely right about the behaviour of the mass, but I was not talking about the mass; I was talking about the wave that runs throught the mass - with the speed of sound, by definition.
The mass itself moves much slower; its mean velocity in the intake tract is less than half the speed of sound.
(If there are any gas dynamic specialists reading in: yes, suction waves move with subsonic speed and pressure waves with supersonic speed, dependent on the magnitude of their amplitude, but for now let's keep it simple ).

aha. I understand your differentiation; this makes sense.
honestly speaking I never realized (and believed) two-stroke is a science on its own. I always took for granted that when you attempt to make a two-stroke engine run well, it was a combination of conducting the right parts, and make sure you cut 95% of the BS running through a paddock. this season we found out that if you dont respect the basis disciplines which make an engine run 'healthy', you are lost in a dessert. (usually this was Emmen for us, after a solid 250km drive. and back obviously).

thanks for sharing your knowledge with us - I have a deep respect

Michael Burgard a écrit:

Hi Guys,
I im just finished testing befor an 1/2 hour.

Michael, may we have a short video, when you will have time?

Thank Frits
But the tests was too much in hurry....
If you can see at the dynosheets the engine got a big breakdown if I do open the valve.I think its because I got to open the valve verry abrupt because if not the reed break direct. At the little time if bin working on this valve I broke 6reeds! .So I think befor continue testing it wuold be important to change my construction of the valve himself,that it could be open slow.I already got some ideas how to builded it,but how I told nasone32 this morning I got really little time at the moment.
But I will try too work each free min. on this project.

@Mark
If I do the engine running the next time with my new valve,the first thing I will do is a nice video!!

Great!



Thank you.